This invention relates to the rotor in a pressure knotter.
In the papermaking process, wood knots and foreign material such as stones or pebbles must be separated from the fluidized pulp. This separation is generally accomplished by passing the fluid pulp through a cylindrical screen whose apertures are sized to reject unwanted solids. During this separation operation, the oversized solids such as knots and pebbles plug the screen apertures. It is known in the prior art to produce periodic hydrodynamic pulses in the direction opposite to the flow of the fluidized pulp through the screen so as to clear the screen. A typical prior art configuration is shown in FIG. 1. In this configuration, hydrofoils 10 carried on a rotor 12 sweep past a screen 14 to clear the screen 14. The hydrofoils 10 are subject to wear at the portion of the hydrofoil near the screen resulting in part from the action of small solid particles which pass through the screen. Because in many commercially available screens the hydrofoils 10 and rotor 12 form a unitary structure, upon wear, the whole rotor/hydrofoil assembly has to be replaced. In other commercially available screening apparatus, the hydrofoil alone is replaced even though only a portion of the hydrofoil experiences wear. Other rotor-blade configurations are shown in U.S. Pat. Nos. 4,200,537; 3,363,759 and 3,680,696 and Canadian Patent No. 1,136,092.